The slightest amount of misalignment between two optical fibers at their connection point generates losses on the signal carried. Consequently, it is extremely important to control the state of alignment and if necessary to be able to adjust it. The core of fibers may be moved out of center with respect to the cladding and accordingly it is not merely sufficient to align claddings with a V-shaped part, for example. Various known control measures have been effected so as to improve the alignment of fibers and reduce losses.
There currently exists a method consisting of measuring the luminous power transmitted by the fibers. Mechanical action is effected on the fibers at the connection point so as to render this luminous power maximum. This technique has the drawback of being sensitive to fluctuations of the luminous power delivered by the source, to possible sensitivity drifts of the detector used for measuring, as well as to the modal distribution of the energy in fibers as regards multimodal fibers.
Another known technique consists of measuring the power diffused at the connection point; by mechanically acting on at least one of the fibers connected, this technique attempts to render this diffused light to a minimum. This technique has the drawback of requiring a decladding of the fibers or the use of claddings transparent to radiation. In addition, the connection parts need to have transparent zones to enable the measurement to be made.
Furthermore, these measurements intended for adjustment between fibers cannot be applied for the single control of a fixed connection, since they require mechanical action on at least one of the fibers so as to cause the transmitted luminous power to vary.
A correct modal alignment is also required when mounting an optical fiber inside a connection plug of the crimped straight plug type.
The operations for adjusting the position of the fiber inside the plug are usually complex and less precise. The tooling required for these operations is described, for example, in the assembly instructions for the PFO tooling set, reference F 780 111 000, and sold by the Radiall company.
The fiber crimped in the plug is mounted declad in a mobile terminal joining piece. The plug is fixed to a support, a panaromic sight being secured to said support.
So as to adjust the position of the fiber in the plug, the core of the fiber is made to coincide with a reticule situated inside the sight. This is a delicate procedure, the first operation consisting of positioning the reticule by means of a standard plug. Having positioned the reticule, the plug to be adjusted is mounted on the support and one extremity of the fiber is illuminated. By acting on the position of the joining piece, the image of the core of the fiber is superimposed on the reticule. Once the position is determined, the fiber is rendered immobile by glueing. The precision obtained by this adjustment is .+-.0.5 micrometers if the fiber is a monomode fiber.